The present invention relates to a hydraulic cylinder and a hydraulic circuit for driving a tool, such as a cutting or stripping knife or spreader arm, which is useful, for example, for enlarging an opening in sheet metal material and to a hydraulic control circuit for operating the cylinder.
In cooperation with tools such as those used in rescue apparatus, as in U.S. Ser. No. 561,190, filed Aug. 1, 1990, entitled "Hydraulically Operated Stripping Device" (F-8187), incorporated herein by reference, it is necessary to make available a functioning total unit including hydraulic cylinder, pump, valves and a cutting and spreading tool within the smallest structural space and to be able to provide a maximum force using this unit.
In a mobile installation, the cylinder is activated by a hand pump. Since the stroke volume of the pump is much smaller than the active volume of the cylinder that is supplied by the pump, hydraulic fluid must be conveyed from an intermediate tank for operating the cylinder. Such units are distributed by FAG Kugelfischer Georg Schafer KGaA, the assignee hereof, under the designation Lukas LKS 35.
In addition to the large amount of space which is required for the separately operated units, there is the disadvantage that the unit cannot be operated in any desired orientation but only the orientations in which the hydraulic fluid covers the intake opening of the pump. Particularly under the frequently rough conditions experienced when the hydraulic system is used in a rescue operation, valuable time may be lost because a suitable operating location must be found for setting up the unit to orient it in order to assure that the pump does not draw in air.
Federal Republic of Germany Published Application OS 36 03 109 discloses a hydraulic hand pump for actuating cable shoe presses and other hydraulic tools. In that case, the working cylinder and the hydraulic pump are arranged coaxially in a common housing. The working cylinder has a high pressure space, while the hand pump comprises a low pressure cylinder having a low pressure piston displaceably arranged within it. There is a concentric bore in the low pressure piston within which is arranged a high pressure piston which defines the limitation of a high pressure cylinder that is present in the low pressure piston. In front of the pump, a pressure fluid supply container is arranged on the housing. That supply container is defined by a flexible diaphragm and is in communication via valves with the low pressure space of the hand pump. That supply container contains the entire volume of hydraulic fluid necessary for operating the hydraulic tool. The diaphragm present in the supply container assures that the intake connection of the pump is surrounded by hydraulic fluid in any position of the unit which avoids the drawing in of air. Since the complete working volume must be stored in the supply tank, the space required in the case of this pump is also high. When high forces are employed and large strokes of the cylinder are required, as are necessary in rescue devices, the unit shown in Federal Republic of Germany OS 36 03 109 is of excessive length so that it is difficult for the operator to handle.